Liquid crystal composition and liquid crystal element

ABSTRACT

A novel smectic liquid crystal composition is disclosed. The smectic liquid crystal composition comprises at least, a dichroic dye, a dual-frequency switchable nematic liquid crystal and a smectic liquid crystal. The dielectric anisotropy of the composition changes from a positive value to a negative value with increasing a frequency of a field applied to the composition. A novel liquid crystal device is also disclosed. The device comprises a pair of electrodes of which at least one is a transparent electrode, and a layer between the pair of electrodes comprising the smectic liquid crystal composition.

This application claims benefit of priority under 35 USC 119 to JapanesePatent Application No. 2005-127981 filed Apr. 26, 2005.

BACKGROUND OF THE INVENTION

1. Technical field

The present invention relates to a liquid crystal composition and aliquid crystal device comprising a liquid crystal layer comprising thecomposition, and more particularly to a liquid crystal deviceadvantageously usable in a liquid crystal device employing a guest-host(hereinafter also referred to as GH) mode.

2. Related art

A display device is required to have a high level of visibility and alow consumption of electric power. As one of display devices having suchqualities, GH-mode display devices, capable of displaying brightly, havebeen known, and is expected as a high-quality display device employing areflective mode.

A liquid crystal composition comprising a dichroic dye having aparticular group and a host liquid crystal, and a liquid crystal deviceemploying a GH-mode are disclosed in Japanese Laid-Open PatentPublication “Tokkai” No. 2004-75821.

The switching of the liquid crystal device is usually carried out byvarying the alignment state while applying (ON) and not applying (OFF)an electric field to liquid crystal. The alignment variation of liquidcrystal without an electric field is affected by a force of alignmentlayer, and, thus, the response speed may become to lower while notapplying an electric field to liquid crystal.

A dual-frequency switching method has been known (see Applied PhysicsLetters, Vol. 25, No. 4, 186-188(1974); and Applied Physics Letters,Vol. 41, No. 8, 697-699(1982)). This method employs a dual-frequencyswitchable liquid crystal, of which dielectric constant anisotropy, Δε,changes from a positive value to a negative value with increasing thefrequency of applied voltage, and therefore allows a reversible changeof the liquid crystal alignment with an electrical field. According tothis method, it is possible to carry out the switching in the mannerthat liquid crystal molecules change their alignment actively, and,thus, to improve the response speed. It is, however, impossible to storeimage information without an electrical field, and, thus, it isnecessary to continue to apply voltage to liquid crystal for maintainingimages.

As a dual-frequency switchable liquid crystal, there has been providedliquid crystal exhibiting a nematic phase (see Mol. Cryst. Liq. Cryst.,49, 83-87 (1978)).

It has been required to provide a liquid crystal device exhibiting ahigh displaying contrast and capable of storing image information.

SUMMARY OF THE INVENTION

One object of the present invention is to provide a liquid crystalcomposition which is useful for preparing a liquid crystal deviceexhibiting a high displaying contrast and capable of storing imageinformation. Another object of the present invention is to provide aliquid crystal device exhibiting a high displaying contrast and capableof storing image information.

Generally, it has been considered that, although a GH-mode employing adual-frequency switchable nematic liquid crystal shows a quickresponsiveness, it cannot store image information without an electricalfield, and, thus, it cannot show a low consumption of electric power tobe required. The inventors conducted various studies, and, as a result,they found that mixing a mixture of dual-frequency switchable nematicliquid crystal with smectic liquid crystal can contribute to improvingbistability. On the basis of the finding, they conducted further variousstudies, and the present invention was achieved.

In one aspect, the present invention provides a smectic liquid crystalcomposition comprising, at least, a dichroic dye, a dual-frequencyswitchable nematic liquid crystal and a smectic liquid crystal, whereina dielectric anisotropy of the composition changes from a positive valueto a negative value with increasing a frequency of a field applied tothe composition.

As embodiments of the invention, there are provided the smectic liquidcrystal composition wherein the smectic liquid crystal is dual-frequencyswitchable; and the smectic liquid crystal composition, wherein, beingapplied a field, a dielectric anisotropy of the smectic liquid crystalchanges from a positive value to a negative value with increasing afrequency of the applied field.

The smectic liquid crystal may be selected from the group presented by afollowing formula (1):T¹-{(D¹)_(e)-L¹}_(m)-(D²)_(k)-T²  Formula (1)

where “Het” represents an oxygen atom or a sulfur atom; B¹ and B²respectively represent a substituted or non-substituted arylene group,heteroarylene group or divalent cycloaliphatic hydrocarbon group; Q¹represents a divalent linking group; C¹ represents a substituted ornon-substituted alkyl group, cycloalkyl group, alkoxy group,alkoxycarbonyl group, acyl group or acyloxy group; j is 0 or 1, p, q andr respectively represent an integer from 0 to 5 and n represents aninteger from 1 to 3, provided that a total number of groups representedby B¹ and B² in the formula (1) is from 3 to 10; in case any of p, q andr is equal to or larger than 2, B¹, Q¹ or B² present in two or moreunits may be same or different to each other; and, in case n is equal toor larger than 2, {(B¹)_(p)-(Q¹)_(q)—(B²)_(r)} present in two or moreunits may be same or different to each other.

The smectic liquid crystal composition may be capable of transforming toa smectic A phase.

The dichroic dye may be selected from the group consisting of azo dyes,anthraquinone dyes and phenoxazine dyes.

The dichroic dye may be selected from compounds having at least onegroup represented by a following formula (2):-(Het)_(j)-{(B¹)_(p)-(Q¹)_(q)-(B²)_(r)}_(n)-C¹  Formula (2)

where “Het” represents an oxygen atom or a sulfur atom; B¹ andB²respectively represent a substituted or non-substituted arylene group,heteroarylene group or divalent cycloaliphatic hydrocarbon group; Q¹represents a divalent linking group; C¹ represents a substituted ornon-substituted, alkyl group, cycloalkyl group, alkoxy group,alkoxycarbonyl group, acyl group or acyloxy group; j is 0 or 1, p, q andr respectively represent an integer from 0 to 5 and n represents aninteger from 1 to 3, provided that a total number of groups representedby B¹ and B² in the formula (2) is from 3 to 10; in case any of p, q andr is equal to or larger than 2, B¹, Q¹ or B² present in two or moreunits may be same or different to each other; and, in case n is equal toor larger than 2, {(B¹)_(p)-(Q¹)_(q)-(B²)_(r)} present in two or moreunits may be same or different to each other.

As embodiments of the invention, there are provided the smectic liquidcrystal composition, wherein the dichroic dye is a compound representedby a formula (3):

where R¹, R², R³, R⁴, R⁵, R⁶, R⁷ and R⁸ respectively represent ahydrogen atom or a substituent group, provide that at least one is agroup represented by -(Het)_(j)-{(B¹)_(p)-(Q¹)_(q)-(B²)_(r)}_(n)-C¹, inwhich “Het” represents an oxygen atom or a sulfur atom, B¹ and B²respectively represent a substituted or non-substituted arylene group,heteroarylene group or divalent cycloaliphatic hydrocarbon group; Q¹represents a divalent linking group; C¹ represents a substituted ornon-substituted, alkyl group, cycloalkyl group, alkoxy group,alkoxycarbonyl group, acyl group or acyloxy group; j is 0 or 1, p, q andr respectively represent an integer from 0 to 5 and n represents aninteger from 1 to 3, provided that a total number of groups representedby B¹ and B² is from 3 to 10; in case any of p, q and r is equal to orlarger than 2, B¹, Q¹ or B² present in two or more units may be same ordifferent to each other; and, in case n is equal to or larger than 2,{(B¹)_(p)-(Q¹)_(q)-(B²)_(r)} present in two or more units may be same ordifferent to each other; and the smectic liquid crystal composition,wherein the dichroic dye is a compound represented by a formula (4):

where R¹¹, R¹², R¹³, R¹⁴, R¹⁵, R¹⁶, and R¹⁷ respectively represent ahydrogen atom or a substituent group, provided that at least one is agroup represented by -(Het)_(j)-{(B¹)_(p)-(Q¹)_(q)-(B²)_(r)}_(n)-C¹, inwhich “Het” represents an oxygen atom or a sulfur atom, B¹ and B²respectively represent a substituted or non-substituted arylene group,heteroarylene group or divalent cycloaliphatic hydrocarbon group; Q¹represents a divalent linking group; C¹ represents a substituted ornon-substituted alkyl group, cycloalkyl group, alkoxy group,alkoxycarbonyl group, acyl group or acyloxy group; j is 0 or 1, p, q andr respectively represent an integer from 0 to 5, and n represents aninteger from 1 to 3, provided that a total number of groups representedby B¹ and B² is from 3 to 10; in case any of p, q and r is equal to orlarger than 2, B¹, Q¹ or B² present in two or more units may be same ordifferent to each other; and, in case n is equal to or larger than 2,{(B¹)_(p)-(Q¹)_(q)-(B²)_(r)} present in two or more units may be same ordifferent to each other.

In another aspect, the present invention provides a liquid crystaldevice comprising:

a pair of electrodes of which at least one is a transparent electrode,and

a layer between the pair of electrodes comprising the smectic liquidcrystal composition of the invention.

As embodiments of the invention, there are provide the liquid crystaldevice, wherein the layer comprises a polymer and the smectic liquidcrystal composition dispersed in the polymer; and the liquid crystaldevice, wherein the layer comprises microcapsules respectivelycomprising the smectic liquid crystal composition.

According to the present invention, it is possible to provide a liquidcrystal device having a high displaying contrast and capable of storingimage information, and a smectic liquid crystal composition useful inproducing the liquid crystal device.

DETAILED DESCRIPTION OF THE EMBODIMENTS

Embodiments of the present invention are described in detail below. Itis to be noted that, in the description, ranges indicated with “to” meanranges including the numerical values before and after “to” as theminimum and maximum values.

The present invention relates to a smectic liquid crystal compositioncomprising, at least, a dichroic dye, a dual-frequency switchablenematic liquid crystal and a smectic liquid crystal wherein a dielectricanisotropy of the composition changes from a positive value to anegative value with increasing a frequency of a field applied to thecomposition; and to a liquid crystal device comprising the smecticliquid crystal composition.

The GH mode liquid crystal device employing a known dual-frequencyswitchable nematic liquid crystal cannot continue to display imageswithout an electric field, and, therefore suffers from having no memoryability. The inventors conducted various studies, and, as a result, theyfound that adding smectic liquid crystal is extremely effective forimproving bistability and storing image information, and on the basis ofthe finding, the present invention was achieved.

[Smectic Liquid Crystal Composition]

The smectic liquid crystal of the present invention comprises at least,one dual-frequency nematic liquid crystal, one smectic liquid crystaland one dichroic dye, and the dielectric anisotropy of the compositionchanges from a positive value to a negative value with increasing afrequency of a field applied to the composition. As well as the nematicliquid crystal, the smectic liquid crystal is preferably selected fromdual-frequency switchable liquid crystals. It is possible to provide aliquid crystal device having a high displaying contrast and capable ofstoring image information by employing such a smectic liquid crystalcomposition. It is also possible to provide a liquid crystal devicewithout an alignment layer, or, in other words, a liquid crystal device,having a simple construction, and, thus, to contribute to simplifying aprocess for producing a liquid crystal device. The liquid crystal devicenot comprising an alignment layer doesn't suffer from light absorptionor light reflection due to an alignment layer, and such a liquid crystaldevice, employing a reflective mode, may have a higher displayingcontrast and yield a higher reflectivity.

Various materials which can be used in the invention will be describedin detail.

At first, the dual-frequency switchable nematic liquid crystal will bedescribed in detail. The “dual-frequency switchable liquid crystal”means a liquid crystal exhibiting a positive dielectric anisotropy whilebeing in an electric field of a low frequency range and exhibiting aninversion to a negative dielectric anisotropy while being in an electricfield of a high frequency range, as detailedly described in LiquidCrystal Device Handbook, Japan Society for the Promotion of Science,Committee 142, p. 189-192 (1989), published by Nikkan Kogyo Shimbun).Specific examples of such liquid crystal include those shown in thefollowing, manufactured by Eastman Kodak Co.

Also commercially available dual-frequency switchable liquid crystalsinclude DF-02XX, DF-05XX, FX-1001 and FX-1002 manufactured by ChissoCo., and MLC-2048 manufactured by F. Merck Inc.

Next, the smectic liquid crystal which can be used in the invention willbe described in detail. The smectic liquid crystal is not to be limitedto the specific types, and can be selected from any liquid-crystallinecompounds exhibiting a smectic phase, is preferably selected fromliquid-crystalline compounds exhibiting a smectic A phase, and is morepreferably selected from dual-frequency switchable liquid-crystallinecompounds exhibiting a smectic phase A. Among such liquid-crystallinecompounds, the compound represented by the following formula (1) isespecially preferred.T¹-{(D¹)_(e)-L¹}_(m)-(D²)_(k)-T²  Formula (1)

In the formula (1), D¹ and D² respectively represent a substituted ornon-substituted, arylene group, heteroarylene group or divalentcycloaliphatic hydrocarbon group.

The arylene group represented by D¹ or D² is preferably selected fromC₆₋₂₀ arylene groups, and more preferably selected from C₆₋₁₀ arylenegroups. Preferred is phenylene or naphthalene-diyl, more preferred issubstituted phenylene, and much more preferred is 1,4-phenylene.

The heteroarylene group represented by D¹ or D² is preferably selectedfrom C₁₋₂₀ heteroarylene groups, and is more preferably selected fromC₂₋₉ heteroarylene groups. Preferred examples of the heteroarylene groupinclude heteroarylene residues which are obtained by removing twohydrogen atoms from a pyridine ring, a quinoline ring, an isoquinolinering, a pyrimidine ring, a pyrazine ring, a thiophene ring, a furanring, an oxazole ring, a thiazole ring, an imidazole ring, a pyrazolering, an oxadiazole ring, a thiadiazole ring and heteroaryl ringscondensed one kind of rings or two or more kinds of rings selectedtherefrom.

The divalent cycloaliphatic hydrocarbon group represented by D¹ or D² ispreferably selected from C₃₋₂₀ divalent cycloaliphatic hydrocarbongroups, and more preferably selected from C₄₋₁₀ divalent cycloaliphatichydrocarbon groups. Preferred is cyclohexane-diyl or cyclopentane-diyl,more preferred is cyclohexane-1,2-diyl, cyclohexane-1,3-diyl,cyclohexane-1,4-diyl or cyclopentane-1,3-diyl; and much more preferredis (E)-cyclohexane-1,4-diyl.

The divalent arylene group, heteroarylene group or cycloaliphatichydrocarbon group represented by D¹ or D²may have one or moresubstituent groups, and such a substituent group may be selected fromSubstituent Group V as shown below.

Substituent Group V:

Halogen atom such as chlorine, bromine, iodine or fluorine atom; amercapto group, a cyano group, a carboxyl group, a phosphoric acidgroup, a sulfo group, a hydroxy group, a C₁₋₁₀, desirably C₂₋₈ and moredesirably C₂₋₅ carbamoyl group such as methylcarbamoyl, ethylcarbamoylor morpholinocarbamoyl; a C₀₋₁₀, desirably C₂₋₈ and more desirably C₂₋₅sulfamoyl group such as methylsulfamoyl, ethylsulfamoyl orpiperidinosulfamoyl; a nitro group; a C₁₋₂₀, desirably C₁₋₁₀ and moredesirably C₁₋₈ alkoxy group such as methoxy, ethoxy, 2-methoxyethoxy or2-phenylethoxy; a C₆₋₂₀, desirably C₆₋₁₂ and more desirably C₆₋₁₀aryloxy group such as phenoxy, p-methylphenoxy, p-chlorophenoxy ornaphthoxy; a C₁₋₂₀, desirably C₂₋₁₂ and more desirably C₂₋₈ acyl groupsuch as acetyl, benzoyl or trichloroacetyl; a C₁₋₂₀, desirably C₂₋₁₂ andmore desirably C₂₋₈ acyloxy group such as acetyloxy or benzoyloxy; aC₁₋₂₀, desirably C₂₋₁₂ and more desirably C₂₋₈ acylamino group such asacetylamino; a C₁₋₂₀, desirably C₁₋₁₀ and more desirably C₁₋₈ sulfonylgroup such as methanesulfonyl, ethanesulfonyl or benzenesulfonyl; aC₁₋₂₀, desirably C₁₋₁₀ and more desirably C₁₋₈ sulfinyl group such asmethanesulfinyl, ethanesulfinyl or benzenesulfinyl; a C₁₋₂₀, desirablyC₁₋₁₂ and more desirably C₁₋₈ substituted or non-substituted amino groupsuch as non-substituted amino, methylamino, dimethylamino, benzylamino,anilino, diphenylamino, 4-methylphenylamino, 4-ethylphenylamino,3-n-propylphenylamino, 4-n-propyl phenylamino, 3-n-butylphenylamino,4-n-butylphenylamino, 3-n-pentylphenylamino, 4-n-pentylphenylamino,3-trifluoro methylphenylamino, 4-trifluoromethylphenylamino,2-pyridylamino, 3-pyridylamino, 2-thiazolylamino, 2-oxazolylamino,N,N-methylphenylamino, N,N-ethyl phenylamino; a C₀₋₁₅, desirably C₃₋₁₀and more desirably C₃₋₆ ammonium group such as trimethylammonium ortriethylammonium; a C₀₋₁₅, desirably C₁₋₁₀ and more desirably C₁₋₆hydrazino group such as trimethylhydrazino; a C₁₋₁₅, desirably C₁₋₁₀ andmore desirably C₁₋₆ ureido group such as non-substituted ureido orN,N-dimethylureido; a C₁₋₁₅, desirably C₁₋₁₀ and more desirably C₁₋₆imide group such as succinimide; a C₁₋₂₀, desirably C₁₋₁₂ and moredesirably C₁₋₈ alkylthio group such as methylthio, ethylthio orpropylthio; a C_(6-80,) desirably C₆₋₄₀ and more desirably C₆₋₃₀arylthio group such as phenylthio, p-methylphenylthio,p-chlorophenylthio, 2-pyridylthio, 1-naphthylthio, 2-naphthylthio,4-propylcyclohexyl-4′-diphenylthio, 4-butylcyclohexyl-4′-diphenylthio,4-pentylcyclohexyl-4′-diphenylthio or 4-propylphenyl-2-ethynyl-4′-diphenylthio; a C₁₋₈₀, desirably C₁₋₄₀ and more desirablyC₁₋₃₀ heteroarylthio group such as 2-pyridylthio, 3-pyridylthio,4-pyridylthio, 2-quinolylthio, 2-frylthio, 2-pyrrolylthio; a C₂₋₂₀,desirably C₂₋₁₂ and more desirably C₂₋₈ alkoxycarbonyl group such asmethoxycarbonyl, ethoxycarbonyl or 2-benzyloxycarbonyl; a C₆₋₂₀,desirably C₆₋₁₂ and more desirably C₆₋₁₀ aryloxycarbonyl group such asphenoxycarbonyl; a C₁₋₁₈, desirably C₁₋₁₀ and more desirably C₁₋₁₅non-substituted alkyl group such as methyl, ethyl, propyl or butyl; aC₁₋₁₈, desirably C₁₋₁₀ and more desirably C₁₋₅ substituted alkyl groupsuch as hydroxylmethyl, trifluoromethyl, benzyl, carboxyethyl,ethoxycarbonylmethyl or acethylamino methyl, of which examples alsoinclude a C₂₋₁₈ (desirably C₃₋₁₀ and more desirably C₃₋₅) unsaturatedhydrocarbon group such as vinyl, ethynyl, 1-cyclohexenel, benzylidine orbenzylidene; a C_(6-20,) desirably C₆₋₁₅ and more desirably C₆₋₁₀substituted or non-substituted aryl group such as phenyl, naphthyl,p-carboxyphenyl, p-nitrophenyl 3,5-dichlorophenyl, p-cyanophenyl,m-fluorophenyl, p-tolyl, 4-propylcyclohexyl-4′-diphenyl,4-butylcyclohexyl-4′-diphenyl, 4-pentylcyclohexyl-4′-diphenyl or4-propylphenyl-2-ethynyl- 4′-diphenyl; and a C₁₋₂₀, desirably C₂₋₁₀ andmore desirably C₄₋₆ substituted or non-substituted heteroaryl group suchas pyridyl, 5-methylpyridyl, thienyl, furyl, morpholino ortetrahydrofurfuryl.

The rings such as benzene or naphthalene ring included in thesubstituents exemplified above may be condensed with other rings.Examples of the substituent also include groups substituted with thesubstituent selected from Substituent Group V.

Among these, as a substituent group of D¹ or D², the exemplified alkylgroup, alkoxy group, halogen atom, hydroxy and cyano are preferred, andthe exemplified alkyl group, halogen atom or cyano are more preferred.

L¹ represents a divalent linking group. L¹ preferably represents analkenylene, an alkynylene, an ether (—O—), an ester (—C(═O)O— or—OC(═O)—), a carbonyl, an azo, an azoxy or an alkyleneoxy; morepreferably represents an ester or an alkyleneoxy.

The alkenylene represented by L¹ is preferably selected from C₂₋₂₀alkenylene groups, and more preferably selected from C₂₋₁₀ alkenylenegroups. Specific examples of the alkenylene include an ethenylene.

The alkynylene represented by L¹ is preferably selected from C₂₋₂₀alkynylene groups, and more preferably selected from C₂₋₁₀ alkynylenegroups. Specific examples of the alkynylene include an ethynylene.

T¹ and T² respectively represent an alkyl group, an alkoxy group, analkoxycarbonyl group, an acyl group, an acyloxy group, a halogen atom ora cyano.

T¹ and T² preferably represent a C₁₋₂₀, more preferably a C₄₋₂₀, andmuch more preferably a C₆₋₁₈ alkyl group; a C₁₋₃₀, more preferablyC₄₋₂₀, and much more preferably C₆₋₁₈ alkoxy group; a C₂₋₃₀, morepreferably a C₅₋₂₁, and much more preferably C₇₋₁₉ alkoxycarbonyl group;a C₂₋₃₀, more preferably a C₅₋₂₁, and much more preferably C₇₋₁₉ acylgroup; a C₂₋₃₀, more preferably a C₅₋₂₁, and much more preferably C₇₋₁₉acyloxy group; a halogen atom or cyano.

The alkyl group, alkoxy group, alkoxycarbonyl group, acyl group oracyloxy group may have one or more substituents, and such a substituentgroup can be selected from Substituent Group V shown above.

Among Substituent Group V, as substituent of T¹ or T², a halogen atom(especially chlorine atom or a fluorine atom), cyano, hydroxyl, alkoxyor acyl are preferred.

Examples of the alkyl group represented by T¹ or T² include octyl,nonyl, decyl, undecyl, dodecyl, octadecyl, 4-cyanobutyl, trifluoromethyland 3-methoxy propyl.

Examples of the alkoxy group represented by T¹ or T² include octyloxy,undecyloxy, dodecyloxy, trifluoromethoxy and 2-methoxy ethoxy.

Examples of the alkoxycarbonyl group represented by T¹ or T² includeoctyloxycarbonyl and dodecyloxycarbonyl.

Examples of the acyl group represented by T¹ or T² include octylcarbonyland dodecylcarbonyl.

Examples of the acyloxy group represented by T¹ or T² includeoctylcarbonyloxy and dodecylcarbonyloxy.

T¹ and T² more preferably represent an alkyl group, an alkoxy group, ahalogen atom or a cyano.

In the formula, “e” represents an integer from 1 to 3, and preferablyrepresents 1 or 2.

In the formula, “m” represents an integer from 1 to 3, and preferablyrepresents 1 or 2.

In the formula, “k” represents 1 or 2.

The sum number of the groups represented by D¹ and D², or, in otherwords, “e×m+k” is 3 to 5, and is preferably 3 or 4. When “e” or “k” is 2or more, plural D¹ or D² are same or different to each other; and when“m” is 2 or more, plural {(D¹)_(e)-L¹} are same or different to eachother.

Preferred combinations of “e”, “m” and “k” are shown below.

(i) e=1, m=2 and k=1;

(ii) e=2, m=1 and k=1;

(iii) e=2, m=1 and k=2.

Examples of the smectic liquid crystal, which can be used in theinvention, include, but not to be limited to, those shown below.

The smectic liquid crystal composition of the invention may comprise oneor more types of nematic liquid crystal that does not show an inversionof the sign of the dielectric anisotropy between a low frequency regionand a high frequency region of the applied electric field. Specificexamples of such the nematic liquid crystal which can be used in theinvention include an azomethine compound, a cyanobiphenyl compound, acyanophenyl ester, a fluorine-substituted phenyl ester, acyclohexanecarboxylate phenyl ester, a fluorine-substitutedcyclohexanecarboxylate phenyl ester, cyanophenylcyclohexane, afluorine-substituted phenylcyclohexane, a cyano-substitutedphenylpyrimidine, a fluorine-substituted phenylpyrimidine, analkoxy-substituted phenylpyrimidine, a fluorine-substituted,alkoxy-substituted phenylpyrimidine, phenyldioxane, a tolan compound, afluorine-substituted tolan compound, and alkenylcyclohexyl benzonitrile.Also there can be employed liquid crystal compounds described in LiquidCrystal Device Handbook, Japan Society for the Promotion of Science,Committee 142, p. 154-192 and 715-722 (1989), Published by Nikkan KogyoShimbun). There can also be employed a fluorine-substituted host liquidcrystal suitable for a TFT drive, such as liquid crystals manufacturedby E. Merck Inc. (such as ZLI-4692, MLC-6267, 6284, 6287, 6288, 6406,6422, 6423, 6425, 6435, 6437, 7700, 7800, 9000, 9100, 9200, 9300 or10000) or liquid crystals manufactured by Chisso Co. (such as LIXON5036xx, 5037xx, 5039xx, 5040xx or 5041xx).

To the smectic liquid crystal composition of the invention, there may beadded a compound not showing a liquid-crystalline property for thepurpose of changing physical properties of the host liquid crystal (suchas a temperature range of the liquid crystal phase, a dielectricanisotropy, a refractive index anisotropy or a cross-over frequency).The term “cross-over frequency” means, in dual-frequency switchableliquid crystal, a frequency at which the dielectric anisotropy changesfrom positive to negative. The liquid crystal composition of theinvention may further contain one or more additives such as a chiralagent, an ultraviolet absorber or an antioxidant. Examples of such anadditive include chiral agents for TN or STN mode, described in LiquidCrystal Device Handbook, Japan Society for the Promotion of Science,Committee 142, p. 199-202 (1989), Published by Nikkan Kogyo Shimbun).

The molar ratio of the dual-frequency switchable nematic liquid crystalto the smectic liquid crystal is not to be limited to a specific range,and preferably falls within the range from 20 mol %/80 mol % to 99 mol%/1 mol %, more preferably falls within the range from 50 mol %/50 mol %to 95 mol %/5 mol %, and much more preferably falls within the rangefrom 70 mol %/30 mol % to 90 mol %/10 mol %.

Next, the dichroic dye which can be used in the invention will bedescribed in detail.

Dichroic dye is defined as a compound to be dissolved in host liquidcrystal and to show a function of absorbing light. The dichroic dye usedin the present invention may have any absorption maximum and anabsorption band, but preferably has an absorption maximum in a yellowregion (Y), a magenta region (M) or a cyan region (C). Also the dichroicdye may be employed singly or in a mixture of plural types. In case ofmixing plural dyes, a mixture of dichroic dyes having an absorptionmaximum in Y, M or C is preferably employed. Known dichroic dyes are,for example, described by A. V. Ivashchenko, “Diachronic Dyes for LiquidCrystal Display”, CRC (1994). Also a method of obtaining a full-colordisplay by mixing a yellow dye, a magenta dye and a cyan dye isdescribed in detail in “Color Chemistry”, Sumio Tokita, Maruzen (1982).The yellow region, magenta region and cyan region mentioned aboverespectively mean a region of 430 to 490 nm, a region of 500 to 580 nmand a region of 600 to 700 nm.

The dichroic dye may be selected from compounds having any chromophoricgroup. Examples of the chromophoric group include azo dye residues,anthraquinone dye residues, perylene dye residues, merocyanine dyeresidues, azomethyne dye residues, phthaloperylene dye residues, indigodye residues, azulene dye residues, dioxazine dye residues,polythiophene dye residues and phenoxazine dye residues. Among these,azo dye residues, anthraquinone dye residues and phenoxazine dyeresidues are preferred, and anthraquinone dye residues and phenoxazinedye, such as phenoxazine-3-one, residues are more preferred.

Examples of the azo dye include monoazo, diazo, trisazo, tetrakisazo andpentakisazo dyes. Among these, monoazo, bisazo or trisazo dyes arepreferred.

The azo dye may contain any ring such as an aromatic ring (for example,benzene ring or naphthalene ring) and a hetero ring (for example,quinoline ring, pyridine ring, thiazole ring, benzothiazole ring,oxazole ring, benzoxazole ring, imidazole ring, bennzoimidazole ring orpyrimidine ring).

The anthraquinone dye desirably has at least one substituent containingan oxygen atom, a sulfur atom or a nitrogen atom, such as an alkoxygroup, an aryloxy group, an alkylthio group, an arylthio group, analkylamino group or an arylamino group. The number of the substituentsincluded in the anthraquinone dye is not limited to any range, and, ingeneral, disubstituted, trisubstituted or tetrakissubstitutedanthraquinone dyes are preferred, and disubstituted or trisubstitutedanthraquinone dyes are more preferred. The substituents may bond to anyposition of anthraquinone rings, and, in general, 1,4-disubstituted,1,5-disubstituted, 1,4,5-trisubstituted, 1,2,4-trisubstituted,1,2,5-trisubstituted, 1,2,4,5-tetrasubstituted and1,2,5,6-tetrasubstituted anthraquinone dyes are preferred.

The dichroic dye, which can be used in the invention, preferably has atleast one group (substituent) represented by a formula (2).-(Het)_(j)-{(B¹)_(p)-(Q¹)_(q)-(B²)_(r)}_(n)-C¹  Formula (2)

In the formula (2), “Het” represents an oxygen atom or a sulfur atom,and preferably a sulfur atom.

In the formula (2), B¹ and B² respectively represent a substituted ornon-substituted, arylene group, heteroarylene group or divalentcycloaliphatic hydrocarbon group.

The arylene group represented by B¹ or B² is desirably selected fromC₆₋₂₀ arylene groups, and is more desirably selected from C₆₋₁₀ arylenegroups. Preferred examples of the arylene group include the divalentresidue of substituted or non-substituted, benzene, naphthalene andanthracene. Divalent residues of benzene or substituted benzene are morepreferred and 1,4-phenylene is especially preferred.

The heteroarylene group represented by B¹ or B² is desirably selectedfrom C₁₋₂₀ heteroarylene groups, and is more desirable selected fromC₂₋₉ heteroarylene groups. Preferred examples of the heteroarylene groupinclude divalent residues which can be obtained by removing two hydrogenatoms from pyridine, quinoline, isoquinoline, pyrimidine, pyrazine,thiophene, furan, oxazole, thiazole, imidazole, pyrazole, oxadiazole,thiadiazole, triazole and heteroaryl rings condensed one kind of ringsor two or more kinds of rings selected therefrom.

The divalent cycloaliphatic hydrocarbon group represented by B¹ or B² isdesirably selected from C₃₋₂₀ divalent cycloaliphatic hydrocarbongroups, and is much more desirably from C₄₋₂₀ divalent cycloaliphatichydrocarbon groups. Preferred examples of the divalent cycloaliphatichydrocarbon group are cyclohexane-diyl and cyclopentane-diyl; morepreferred examples are cyclohexane-1,2-diyl, cyclohexane-1,3-diyl,cyclohexane-1,4-diyl and cyclopentane-1,3-diyl; and the most preferredexample is (E)-cyclohexane-1,4-diyl.

The arylene group, heteroarylene group or divalent cycloaliphatichydrocarbon represented by B¹ or B² may have one or more substituents,and such a substituent group is desirably selected from SubstituentGroup V described above. Among those, the exemplified alkyl group, arylgroup, alkoxy group, aryloxy group, halogen atom, amino, substitutedamino group, hydroxyl, alkylthio group and arylthio group are preferred,and the exemplified alkyl group, aryl group and halogen atom are morepreferred.

In the formula (2), Q¹ represents a divalent linking group. Q¹ mayconsist of at least one atom selected from carbon atom, nitrogen atom,oxygen atom or sulfur atom.

The linking group represented by Q¹ preferably represents a C₀₋₆₀divalent linking group, more preferably represents a C₀₋₃₀ divalentlinking group, and much more preferably represents a C₀₋₂₀ divalentlinking group. Preferred examples of the liking group represented by Q¹include linking groups consisting of one or a combination of two or moreselected from the group consisting of an alkylene group, an alkenylenegroup, an alkynylene group, an amide group (—NH—), an ether group (—O—),an ester group (—COO— or —OCO—), a sulfonamide group (—SO₂NH—), a ureidogroup (—NH—CO—NH—), a sulfonyl group (—SO₂—), a sulfinyl group (—SO—), athioether group (—s—), a carbonyl group (—CO—), —NR— (where R is ahydrogen atom, an alkyl group or an aryl group), an azo group (—N₂—), anazoxy group (—N₂(O)—) and a divalent heterocyclic group.

The alkylene group represented by Q¹ is preferably selected from C₁₋₂₀alkylene groups, and is more preferably selected from C₁₋₁₀ alkylenegroups. Specific examples of the alkylene group include methylene,ethylene, propylene, butylene, pentylene and cyclohexyl-1,4-diyl.

The alkenylene group represented by Q¹ is preferably selected from C₂₋₂₀alkenylene groups, and is more preferably selected from C₂₋₁₀ alkenylenegroups. Specific examples of the alkenylene group include ethenylene.

The alkynylene group represented by Q¹ is preferably selected from C₂₋₂₀alkynylene groups, and is more preferably selected from C₂₋₁₀ alkynylenegroups. Specific examples of the alkynylene group include ethynylene.

The alkyl group represented by R in —NR— is preferably selected fromC₁₋₂₀ alkyl groups, and is more preferably selected from C₁₋₁₀ alkylgroups. The aryl group represented by R in —NR— is preferably selectedfrom C₆₋₁₄ aryl groups, and is more preferably selected from C₆₋₁₀ arylgroups.

The divalent heterocyclic group represented by Q¹ is preferably selectedfrom C₂₋₂₀ divalent heterocyclic groups, and is much more preferablyselected from C₄₋₁₀ divalent heterocyclic groups. Specific examples ofthe divalent heterocyclic group include piperazine-1,4-diyl.

Q¹ is desirably an alkylene group, an alkenylene group, an alkynylenegroup, an ether group, a thioether group, an amide group, an estergroup, a carbonyl group or a combination thereof. And Q¹ is moredesirably an alkylene group, alkynylene group, an ether group, an amidegroup, an ester group or a carbonyl group.

Q¹ may carry a substituent group selected from Substituent Group Vdescribed above.

In the formula (2), C¹ represents a substituted or non-substituted,alkyl group, cycloalkyl group, alkoxy group, alkoxycarbonyl group, acylgroup or acyloxy group.

C¹ preferably represents a C₁₋₃₀, more preferably C₁₋₁₂ and much morepreferably C₁₋₈ alkyl and cycloalkyl group; a C₁₋₂₀, more preferablyC₁₋₁₀ and much more preferably C₁₋₈ alkoxy group; a C₁₋₂₀, morepreferably C₂₋₁₂ and much more preferably C₂₋₈ acyloxy group; a C₁₋₃₀,more preferably C₁₋₁₂ and much more preferably C₁₋₈ acyl group; or aC₂₋₂₀, more preferably C₂₋₁₂ and much more preferably C₂₋₈alkoxycarbonyl group.

Specific examples of the alkyl group and cycloalkyl group represented byC¹ include methyl, ethyl, propyl, butyl, t-butyl, i-butyl, s-butyl,pentyl, t-pentyl, hexyl, heptyl, octyl, cyclohexyl, 4-methylcyclohexyl,4-ethylcyclohexyl, 4-propylcyclohexyl, 4-butylcyclohexyl,4-pentylcyclohexyl, hydroxymethyl, trifluoromethyl and benzyl.

Specific examples of the alkoxy group include methoxy, ethoxy, 2-methoxyethoxy and 2-phenylethoxy.

Specific examples of the acyloxy group include acetyloxy and benzoyloxy.

Specific examples of the acyl group include formyl, acetyl pivaloyl,2-chloroacetyl, stearoyl, benzoyl and p-n-octyloxyphenylcarbonyl.

Specific examples of the alkoxycarbonyl group include methoxycarbonyl,ethoxycarbonyl and 2-benzyloxycarbonyl.

C¹ is desirably selected from a substituted or non-substituted alkylgroup or a substituted or non-substituted alkoxy group, and moredesirably selected from ethyl, propyl, butyl, pentyl, hexyl, ortrifluoromethoxy.

C¹ may carry one or more substituents selected from Substituent Group Vdescribed above.

The alkyl group represented by C¹ may carry one or more substituentsselected from Substituent Group V described above, and preferredexamples of the substituent of the alkyl group include the exemplifiedhalogen atom, cyano, hydroxy, carbamoyl, alkoxy, aryloxy, acyl, acyloxy,acylamino, amino, alkylthio, arylthio, heteroarylthio, alkoxycarbonyland aryloxycarbonyl.

The cycloalkyl group represented by C¹ may carry one or moresubstituents selected from Substituent Group V described above, andpreferred examples of the substituent of the cycloalkyl group includethe exemplified halogen atom, cyano, hydroxy, carbamoyl, alkoxy,aryloxy, acyl acyloxy, acylamino, amino, alkylthio, arylthio,heteroarylthio, alkoxycarbonyl, aryloxycarbonyl and alkyl.

The alkoxy group represented by C¹ may carry one or more substituentsselected from Substituent Group V described above, and preferredexamples of the substituent of the alkoxy group include the exemplifiedhalogen atom (especially fluorine atom), cyano, hydroxy, carbamoyl,alkoxy, aryloxy, acyl acyloxy, acylamino, amino, alkylthio, arylthio,heteroarylthio, alkoxycarbonyl and aryloxycarbonyl.

The alkoxycarbonyl group represented by C¹ may carry one or moresubstituents selected from Substituent Group V described above, andpreferred examples of the substituent of the alkoxycarbonyl groupinclude the exemplified halogen atom, cyano, hydroxy, carbamoyl, alkoxy,aryloxy, acyl, acyloxy, acylamino, amino, alkylthio, arylthio,heteroarylthio, alkoxycarbonyl and aryloxycarbonyl.

The acyl group represented by C¹ may carry one or more substituentsselected from Substituent Group V described above, and preferredexamples of the substituent of the acyl group include the exemplifiedhalogen atom, cyano, hydroxy, carbamoyl, alkoxy, aryloxy, acyl, acyloxy,acylamino, amino, alkylthio, arylthio, heteroarylthio, alkoxycarbonyland aryloxycarbonyl.

The acyloxy group represented by C¹ may carry one or more substituentsselected from Substituent Group V described above, and preferredexamples of the substituent of the acyloxy group include the exemplifiedhalogen atom, cyano, hydroxy, carbamoyl, alkoxy, aryloxy, acyl, acyloxy,acylamino, amino, alkylthio, arylthio, heteroarylthio, alkoxycarbonyland aryloxycarbonyl.

In the formula (2), j represents 0 or 1, and is preferably 0.

In the formula (2), p, q and r respectively represent an integer from 0to 5; and n represents an integer from 1 to 3, provided that a totalnumber of groups represented by B¹ and B² is from 3 to 10, and ispreferably from 3 to 5.

In case any of p, q and r is equal to or larger than 2, B¹, Q¹ or B²present in two or more units may be same or different to each other;and, in case n is equal to or larger than 2,{(B¹)_(p)-(Q¹)_(q)-(B²)_(r)} present in two or more units may be same ordifferent to each other.

Preferred combinations of p, q and r are shown below:

(i) P=3, q=0, r=0 and n=1;

(ii) P=4, q=0, r=0 and n=1;

(iii) P=5, q=0, r=0 and n=1;

(iv) P=2, q=0, r=1 and n=1;

(v) P=2, q=1, r=1 and n=1;

(vi) P=1, q=1, r=2 and n=1;

(vii) P=3, q=1, r=1 and n=1;

(viii) P=2, q=0, r=2 and n=1;

(ix) P=1, q=1, r=1 and n=2;

(x) P=2, q=1, r=1 and n=2;

Especially preferred combinations are (i) P=3, q=0, r=0 and n=1; (iv)P=2, q=0, r=1 and n=1; and (v) P=2, q=1, r=1 and n=1.

The group (substituent) represented by the formula of-{(B)_(p)-(Q¹)_(q)-(B²)_(r)}_(n)-C¹ preferably containing structuresexhibiting liquid crystallinity. The structures may exhibit any kind ofliquid crystallinity, however, preferably nematic, smectic, or discoticliquid crystallinity, more preferably nematic or smectic liquidcrystallinity.

Specific examples of the group (substituent) represented by the formulaof -{(B¹)_(p)-(Q¹)_(q)-(B²)_(r)}_(n)-C¹ will be listed below, which byno means restricts the present invention. In the following formulae,wave lines denote portions of bonding to Het.

The dichroic dye to be used in the present invention desirably has atleast one, more desirably 1 to 8, much more desirably 1 to 4 and furthermuch more desirably 1 or 2 substituents represented by the formula“-(Het)_(j)-{(B¹)_(p)-(Q¹)_(q)-(B²)_(r)}_(n)-C¹”.

Preferred examples of the group represented by the formula (2) are asfollows:

[1] “Het” is a sulfur atom, B¹ is a substituted or non-substitutedarylene or heteroarylene group, B² is a cyclohexane-1,4-diyl group, C¹is a substituted or non-substituted alkyl group, j=1, p=2, q=0, r=1 andn=1; and

[2] “Het” is a sulfur atom, B¹ is a substituted or non-substitutedarylene or heteroarylene group, B² is a cyclohexane-1,4-diyl group, C¹is a substituted or non-substituted alkyl group, j=1, p=1, q=0, r=2 andn=1.

More preferred examples of the group represented by the formula (2) areas follows:

[3] “Het” is a sulfur atom, B¹ is a substituted or non-substituted1,4-phenylene group, B² is a trans-cyclohexyl group, C¹ is a substitutedor non-substituted alkyl group (preferably methyl, ethyl, propyl, butyl,pentyl or hexyl), j=1, p=2, q=0, r=1 and n=1, or, in other words, agroup represented by a formula (a-1) shown below; and

[4] “Het” is a sulfur atom, B¹ is a substituted or non-substituted1,4-phenylene group, B² is a trans-cyclohexane-1,4-diyl group, C¹ is asubstituted or non-substituted alkyl group (preferably methyl, ethyl,propyl, butyl, pentyl or hexyl), j=1, p=1, q=0, r=2 and n=1, or, inother words, a group presented by a formula (a-2) shown below.

In the formulae, R^(a1) to R^(a12) respectively represent a hydrogenatom or a substituent group. The substituent is selected fromSubstituent Group V described above. It is preferred that R^(a1) toR^(a12) respectively represent a hydrogen atom, a halogen atom(preferably fluorine atom), a substituted or non-substituted alkylgroup, a substituted or non-substituted aryl group or a substituted ornon-substituted alkoxy group.

The preferred alkyl group, aryl group or alkoxy group respectivelyrepresented by R^(a1) to R^(a12) are same as those exemplified inSubstituted Group V.

In the formulae, C^(a1) and C^(a2) respectively represent a substitutedor non-substituted alkyl group, preferably a substituted ornon-substituted C₁₋₂₀ alkyl group, much more preferably a substituted ornon-substituted C₁₋₁₀ alkyl group, especially preferably methyl, ethyl,propyl, butyl, pentyl or hexyl.

The dichroic dye may be selected from azo dyes. Examples of the azo dyeinclude monoazo, diazo, trisazo, tetrakisazo and pentakisazo dyes. Amongthese, monoazo, bisazo or trisazo dyes are preferred.

Any azo dyes, containing any ring such as an aromatic ring (e.g. benzenering and naphthalene ring) and a hetero ring (e.g. quinoline ring,pyridine ring, thiazole ring, benzothiazole ring, oxazole ring,benzoxazole ring, imidazole ring, benzoimidazole ring and pyrimidinering), can be used in the invention. Among these, azo dyes carrying thegroup represented by the formula (2) are preferred.

The dichroic dye may be selected from anthraquinone dyes. Anthraquinonedyes carrying one or more groups containing an oxygen atom, a nitrogenatom or a sulfur atom are preferred, and the anthraquinone dyes carryingan alkoxy group, an aryloxy group, an alkylthio group, an arylthiogroup, an alkylamino group, arylamino group or the like are morepreferred. The number of the substituents included in the anthraquinonedye is not limited to any range, and, in general, disubstituted,trisubstituted or tetrakissubstituted anthraquinone dyes are preferred,and disubstituted or trisubstituted anthraquinone dyes are morepreferred. The substituents may bond to any position of anthraquinonerings, and, in general, 1,4-disubstituted, 1,5-disubstituted,1,4,5-trisubstituted, 1,2,4-trisubstituted, 1,2,5-trisubstituted,1,2,4,5-tetrasubstituted and 1,2,5,6-tetrasubstituted anthraquinone dyesare preferred. Among these, anthraquinone dyes carrying the grouprepresented by the formula (2) are preferred.

The dichroic dye which can be used in the invention desirably selectedfrom anthraquinone dyes represented by a formula (3) shown below.

In the formula (3), at least one of R¹, R², R³, R⁴, R⁵, R⁶, R⁷ and R⁸ isa group (substituent) represented by-(Het)_(j)-{(B¹)_(p)-(Q¹)_(q)-(B²)_(r)}_(n)-C¹, and others represent ahydrogen atom or a substituent group.

In the group of -(Het)_(j)-{(B¹)_(p)-(Q¹)_(q)-(B²)_(r)}_(n)-C¹, “Het”represents an oxygen atom or a sulfur atom; B¹ and B² respectivelyrepresent a substituted or non-substituted, arylene group, heteroarylenegroup or divalent cycloaliphatic hydrocarbon group; Q¹ represents adivalent linking group; C¹ represents a substituted or non-substituted,alkyl group, cycloalkyl group, alkoxy group, alkoxycarbonyl group, acylgroup or acyloxy group; j is 0 or 1, p, q and r respectively representan integer from 0 to 5, and n represents an integer from 1 to 3,provided that a total number of groups represented by B¹ and B² is from3 to 10; in case any of p, q and r is equal to or larger than 2, B¹, Q¹or B² present in two or more units may be same or different to eachother; and, in case n is equal to or larger than 2,{(B¹)_(p)-(Q¹)_(q)-(B²)_(r)} present in two or more units may be same ordifferent to each other.

In the formula (3), “Het”, B¹, B², Q¹, C¹, j, p, q, r and n have samepreferred ranges as in the formula (2).

The substituent represented by R¹, R², R³, R⁴, R⁵, R⁶, R⁷ or R⁸ may beselected from Substituent Group V, and is preferably selected from thegroup consisting of the exemplified halogen atom, mercapto, hydroxy,carbamoyl, sulfamoyl, nitro, alkoxy, aryloxy, acyloxy, acylamino, amino,alkylthio, arylthio, heteroarylthio, alkoxycarbonyl, aryloxycarbonyl,alkyl, aryl and heteroaryl; and is more preferably selected from thegroup consisting of the exemplified halogen atom, hydroxy, nitro,alkoxy, aryloxy, acyloxy, amino, alkylthio, arylthio, heteroarylthio,alkoxycarbonyl, aryloxycarbonyl, alkyl, aryl and heteroaryl.

One preferred example is a compound of the formula (3) in which at leastone of R¹, R⁴, R⁵ and R⁸ is the group represented by-(Het)_(j)-{(B¹l)_(p)-(Q¹)_(q)-(B²)_(r)}_(n)-C¹.

The dichroic dye may be selected from phenoxazine dyes. The phenoxazine(phenoxazine-3-one) dyes carrying one or more groups containing anoxygen atom, a sulfur atom or a nitrogen atom are preferred, and thephenoxazine dyes carrying an alkoxy group, an aryloxy group, analkylthio group, an arylthio group, an alkylamino group, arylamino groupor the like are more preferred; and the phenoxazine dyes carrying one ormore groups represented by the formula (2) are much more preferred.

The phenoxazine dye represented by the formula (4) is much morepreferred.

In the formula, at least one of R¹¹, R¹², R¹³, R¹⁴, R¹⁵, R¹⁶, and R¹⁷represents a group (substituent) represented by-(Het)_(j)-{(B¹)_(p)-(Q¹)_(q)-(B²)_(r)}_(n)-C¹, and others represent ahydrogen atom or a substituent group.

In the group of -(Het)_(j)-{(B¹)_(p)-(Q¹)_(q)-(B²)_(r)}_(n)-C¹, “Het”represents an oxygen atom or a sulfur atom; B¹ and B² respectivelyrepresent a substituted or non-substituted, arylene group, heteroarylenegroup or divalent cycloaliphatic hydrocarbon group; Q¹ represents adivalent linking group; C¹ represents a substituted or non-substituted,alkyl group, cycloalkyl group, alkoxy group, alkoxycarbonyl group, acylgroup or acyloxy group; j is 0 or 1, p, q and r respectively representan integer from 0 to 5, and n represents an integer from 1 to 3,provided that a total number of groups represented by B¹ and B² is from3 to 10; in case any of p, q and r is equal to or larger than 2, B¹, Q¹or B² present in two or more units may be same or different to eachother; and, in case n is equal to or larger than 2,{(B¹)_(p)-(Q¹)_(q)-(B²)_(r)} present in two or more units may be same ordifferent to each other.

In the formula (3), “Het”, B¹, B², Q¹, C¹, j, p, q, r and n have samepreferred ranges as in the formula (2).

The substituent represented by R¹¹, R¹², R¹³, R¹⁴, R¹⁵, R¹⁶, or R¹⁷ maybe selected from Substituent Group V, and is preferably selected fromthe group consisting of the exemplified amino, halogen atom, hydroxy,cyano, carbamoyl, sulfamoyl, alkoxy, aryloxy, acyloxy, acylamino,ureido, imide, alkylthio, arylthio, heteroarylthio, alkoxycarbonyl,aryloxycarbonyl, alkyl, aryl and heteroaryl; and is more preferablyselected from the group consisting of the exemplified amino, halogenatom, hydroxy, carbamoyl, acyloxy, acylamino, imide, alkylthio,arylthio, heteroarylthio, alkoxycarbonyl, aryloxycarbonyl, alkyl andaryl.

One preferred example is a compound of the formula (4) in which at leastone of R¹¹, R¹⁴, and R¹⁶ is the group represented by-(Het)_(j)-{(B¹)_(p)-(Q¹)_(q)-(B²)_(r)}_(n)-C¹.

Examples of the dichroic anthraquinone dye and the dichroic phenoxazinedye, which can be used in the invention, include, however not to belimited to, the compounds shown below.

Examples of the dichroic azo dye, which can be used in the invention,include, however not to be limited to, the compounds shown below.

Examples of the dichroic dioxazine dye and the merocyanine dye, whichcan be used in the invention, include, however not to be limited to, thecompounds shown below.

The dichroic dyes carrying a group represented by the formula (2) can beprepared according to any known process or the combination of knownprocesses. For example, the dyes can be prepared according to theprocess described in Japanese Laid-Open Patent Publication “Tokkai” No.2003-192664.

In the smectic liquid crystal composition of the invention, a ratio ofthe dichroic dye to the host liquid crystal, which is a mixture of adual-frequency switchable nematic liquid crystal and a smectic liquidcrystal, the term “host liquid crystal” being used with the same meaninghereinafter, is not to be limited to a specific range, and is preferablyfrom 0.1 to 15 wt % and particularly preferably 0.5 to 6 wt %.

The dissolving of the dichroic dye into the host liquid crystal can beachieved by a mechanical agitation, a heating, an ultrasonic waveapplication or a combination thereof. The smectic liquid crystalcomposition of the invention may be prepared by employing knowntechniques.

[Liquid Crystal Device]

The liquid crystal device of the invention comprises a pair ofelectrodes of which at least one is a transparent electrode, and a layerbetween the pair of electrodes comprising a smectic liquid crystalcomposition of the invention. The embodiment of the smectic liquidcrystal composition contained in the layer is not to be limited to aspecific embodiment, and the layer may be formed of the smectic liquidcrystal layer; may comprise a polymer and the smectic liquid crystalcomposition dispersed in the polymer; or may comprise microcapsulesrespectively comprising the smectic liquid crystal composition.

The liquid crystal composition of the invention is preferably employedin a GH-mode displaying device. A GH mode displaying device comprising acell filled with a liquid crystal composition, prepared by dissolvingdichroic dye in host liquid crystal, can generally display imageswithout a polarizing plate, because the absorption state of the cell ischanged by an electric field applied to the cell, thereby displayingimages. Applying an electric field, the orientation of the host liquidcrystal in the cell is changed, and the orientation of the dichroic dyeis changed as well as the host liquid crystal, and, therefore, theabsorption state of the cell is changed. It is generally considered thatGH-mode displaying devices can display brighter images compared withother displaying devices employing a polarizing plate.

As a substrate of the electrode substrate, which can be used in theinvention, is usually selected from glass or plastic substrates, ispreferably selected from plastic films. Examples of the plastic filmsinclude films of acrylic polymer, polycarbonate, and epoxy basedpolymer. More specific examples of the substrate include triacetycellulose (TAC) films, polyethylene terephthalate (PET) films,polyethylene naphthalate (PEN) films, syndiotactic polystyrene (SPS)films, polyphenylene sulfide (PPS) films, polycarbonate (PC) films,polyarylate (PAr) films, polysulfone (PSF) films, polyester sulfone(PES) films, polyether imide (PEI) films, cyclic polyolefin films andpolyimide (PI) films. The substrate is more preferably selected frompolyethylene terephthalate (PET) films.

The thickness of the plastic substrate is not to be limited a specificrange, and preferably from 30 μm to 700 μm, more preferably from 40 μmto 200 μm, and much more preferably from 50 μm to 150 μm. The haze ofthe substrate is preferably not greater than 3%, more preferably notgreater than 2% and much more preferably not greater than 1%. And theoptical transmittance of the substrate is preferably not lower than 70%,is more preferably not lower than 80%, and is much more preferably notlower than 90%.

One or more additives such as plasticizers, dyes, pigments, antistaticadditives, ultraviolet absorbers, antioxidant agents, inorganic fineparticles, peel-promoting agents, leveling agents and lubricants may beadded to the plastic substrate without lowering the effect of theinvention.

Transparent and untransparent plastic substrates may be used in theinvention. As an untransparent plastic substrate, white substrateshaving light reflectivity can be used. Examples of the white substrateinclude plastic films containing inorganic pigments such as titaniumoxide and zinc oxide. In the case that the displaying surface is asurface of the substrate, the substrate may be required to betransparent to at least visible light.

The substrate is described for example in Liquid Crystal DeviceHandbook, Japan Society for the Promotion of Science, Committee 142, p.218-231 (1989), Published by Nikkan Kogyo Shimbun).

On at least one of the pair of substrates, there is formed an electrodelayer, which is preferably an transparent electrode. The electrode layermay be formed of indium oxide, indium tin oxide (ITO), or tin oxide. Thetransparent electrode can for example be those described in LiquidCrystal Device Handbook, Japan Society for the Promotion of Science,Committee 142, p. 232-239 (1989), Published by Nikkan Kogyo Shimbun).

The transparent electrode may be formed by a sputtering method, asol-gel method or a printing method.

The liquid crystal device of the invention is preferably provided with alayer, subjected to an alignment process for the purpose of aligning theliquid crystal, on a surface of the substrate in contact with the liquidcrystal. Such alignment process may be carried out by coating andaligning a quaternary ammonium salt, by coating polyimide and rubbing asurface of the polyimide layer, by an oblique evaporation of SiO₂, or bya light irradiation utilizing photoisomerization. An alignment film canfor example be those described in Liquid Crystal Device Handbook, JapanSociety for the Promotion of Science, Committee 142, p. 240-256 (1989),Published by Nikkan Kogyo Shimbun).

It is to be noted that, according to the liquid crystal device of theinvention, it is possible to carry out the switching of the orientationof the liquid crystal only with variation of applying voltage without analignment layer, because it employs the dual-frequency switchablesmectic liquid crystal composition of the invention. And, thus, theliquid crystal device of the invention may comprise or not comprise analignment layer, and the liquid crystal device without an alignmentlayer has advantages to be simplified its structure and to be free fromlowering of the display properties due to the presence of an alignmentlayer.

The liquid crystal device of the invention can be produced by forming agap of 1 to 50 μm between the substrates for example by means of aspacer, and filling the gap with the liquid crystal composition of theinvention. The employable spacer is described for example in LiquidCrystal Device Handbook, Japan Society for the Promotion of Science,Committee 142, p. 257-262 (1989), Published by Nikkan Kogyo Shimbun).The liquid crystal composition of the invention can be provided in aspace between the substrates, by coating or printing on the substrate.

The liquid crystal device of the invention can be driven by a simplematrix drive method, or by an active matrix drive method utilizing forexample a thin film transistor (TFT). Such drive methods are describedin detail for example in Liquid Crystal Device Handbook, Japan Societyfor the Promotion of Science, Committee 142, p. 387-460 (1989),Published by Nikkan Kogyo Shimbun), and can be utilized for driving theliquid crystal device of the invention.

For driving the liquid crystal device of the invention, voltages of alow frequency region and a high frequency region may be employed. Afrequency range of the voltage to be applied to the liquid crystal layeris variable depending on a type of the liquid crystal to be employed,and a cross-over frequency of such liquid crystal, but, in general, ispreferably within a range of 0.1 Hz to 10 MHz, and more preferably 1 Hzto 1 MHz. A frequency in the low frequency region is preferably 0.1 Hzto 100 kHz, more preferably 1 Hz to 10 kHz and further preferably 10 Hzto 10 kHz. Also a frequency in the high frequency region is preferably100 Hz to 10 MHz, more preferably 100 Hz to 1 MHz and further preferably1 kHz to 1 MHz.

The liquid crystal display utilizing the liquid crystal device of theinvention may be of any type. And the liquid crystal device of theinvention is applicable to a laminated GH mode described for example inJPA Nos. 10-67990, 10-239702, 10-133223, 10-339881, 11-52411, 11-64880and 2000-221538 (the term “JPA” as used herein means an “unexaminedpublished Japanese patent application (Kohkai Tokkyo Kohou)”). Theliquid crystal device of the invention is also applicable to a GH modeutilizing microcapsules as described in JPA No. 11-24090. Thus, anembodiment of the liquid crystal device of the invention is a GH modeliquid crystal device having a liquid crystal layer between a pair ofelectrodes of which at least either is a transparent electrode, whereinthe liquid crystal layer includes microcapsules containing the liquidcrystal composition of the invention. Furthermore, liquid crystal deviceof the invention is applicable to a GH mode of polymer dispersed liquidcrystal type, as described in JPA Nos. 5-61025, 5-265053, 6-3691,6-23061, 5-203940, 6-242423, 6-289376, 8-278490 and 9-813174. Thus, anembodiment of the liquid crystal device of the invention is a GH modeliquid crystal device of polymer dispersed liquid crystal type, having apolymer medium layer between a pair of electrodes of which at leasteither is a transparent electrode, wherein the polymer medium layerincludes a polymer, and a liquid crystal composition of the inventiondispersed in the polymer.

The liquid crystal device of the invention may utilize a liquid crystalcomposition containing plural dichroic dyes. Also the liquid crystalcomposition may have any color. Also in case of forming a black-coloredliquid crystal composition for example by mixing plural dichroic dyes,it can be utilized in a liquid crystal device for displaying white andblack colors by a voltage application. It is also possible to prepare aliquid crystal device for color display by preparing liquid crystalcompositions colored in red, green and blue and arranging such threecompositions in parallel manner on a substrate. Also the liquid crystaldevice of the invention may have a laminate structure. For example therecan be employed a three-layered structure respectively formed byyellow-, magenta- and cyan-colored liquid crystal compositions; atwo-layered structure constituted of a layer formed by a parallelarrangement of yellow, magenta and cyan colored liquid crystalcompositions and a layer formed by a parallel arrangement of liquidcrystal compositions of complementary colors of blue, green and red; anda two-layered structure constituted of a layer of a black-colored liquidcrystal composition and a layer formed by a parallel arrangement ofliquid crystal compositions of blue, green and red.

EXAMPLES

The following examples further illustrate the present invention. Thematerials, reagents, amounts and proportions thereof, procedures or thelike shown in the following examples can be appropriately changedwithout departing from the spirit of the present invention. Therefore,the scope of the present invention is not limited to the specificexamples shown below.

Example 1

(Synthesis. No. 1 of Smectic Liquid Crystal)

Smectic liquid crystal (1) was prepared according to a scheme shownbelow.

(Synthesis of Compound 1a)

A 600 ml of acetonitrile solution of 4-hydroxy benzoic acid (30 g)(manufactured by TOKYO CHEMICAL INDUSTRY CO., LTD.) and CsF-Celite(109.4 g), which was prepared according to a method described inSYNTHETIC COMMUNICATIONS, 28(11), 2021-2026 (1998) was added dropwisewith 74.3 g of benzyl bromide, and was stirred under reflux for threehours. The reaction solution was condensed under reduced pressure, addedwith 500 ml of ethyl acetate, and filtered. The filtrate was condensedunder reduced pressure, and the condensed residue was recrystallized ina mixed solvent of water and methanol to yield a crude crystal. Thecrude crystal was recrystallized in toluene to yield 31 g of Compound1a.

(Synthesis of Compound 1b)

A 50 ml of methylene chloride of Compound 1a (4 g) and 4-n-undecyloxybenzoic acid (5.1 g) (manufactured by TOKYO CHEMICAL INDUSTRY CO.,LTD.), was added dropwise with a 30 ml of methylene chloride solution ofdicyclo carbodiimide (4.3 g), and was stirred under reflux for one hour.The reaction solution was poured into a mixture of ethyl acetate andhydrochloric acid (1 N), and separated into an organic layer and a waterlayer. The organic layer was washed with hydrochloric acid (1 N), driedwith magnesium sulfate, and condensed under reduced pressure. Thecondensed residue was purified with silica gel chromatography(developing solvent: a mixed solvent of ethyl acetate and hexane (1/5)),to yield Compound 1b (7.4 g).

(Synthesis of Compound 1c)

The mixed solution of a 70 ml of isopropyl alcohol and a 10 ml oftetrahydrofuran (THF) of Compound 1b (7 g) was added with 10% Pd/C (1.0g), and stirred under atmospheric pressure with hydrogen addition forfour hours. The reaction solution was filtered through sellite, andcondensed under reduced pressure. The condensed residue wasrecrystallized in isopropyl alcohol to yield 5.0 g of Compound 1c.

(Synthesis of Smectic Liquid Crystal (1))

A 50 ml of chloroform solution of Compound 1c (2.0 g), 4-cyano phenol(0.58 g) (manufactured by TOKYO CHEMICAL INDUSTRY CO., LTD.) anddimethylamino pyridine (0.12 g) was added dropwise with a 10 ml ofmethylene chloride solution of dicyclohexyle carbodiimide (1.2 g), andstirred under reflux for one hour. The reaction solution was poured intoa mixture of chloroform and hydrochloric acid (1 N), and separated intoan organic layer and a water layer. The organic layer was washed withhydrochloric acid (1 N), dried with magnesium sulfate, and condensedunder reduced pressure. The condensed residue was purified with silicagel chromatography (developing solvent: chloroform), to yield a crudecrystal. The crude crystal was recrystallized in isopropyl alcohol toyield 2.0 g of Smectic Liquid Crystal (1). The compound was identifiedby element analysis, NMR measurement and mass spectrum measurement. Theappearance of the compound was a white solid. Measuring the transitiontemperatures of Smectic Liquid Crystal (1), it was found that atransition temperature from a crystal phase to a smectic A phase was107° C. and a transition temperature from a smectic A phase to anisotropic phase was 199° C.

Anisotropy of Refractive Index Δn:

-   -   Δn=0.23 (the value was calculated by an extrapolation sing        liquid crystal “ZLI-1132” manufactured by Merck & Co., Ltd.)

¹H-NMR (CDCl₃)

-   -   δ:0.88(3H,t), 1.28(14H,m), 1.49(2H,m), 1.83(2H,m), 4.05(2H,t),        7.02(2H,d), 7.39(4H,m), 7.76(2H,d), 8.15(2H,d), 8.28(2H,d).        (Synthesis No. 2 of Smectic Liquid Crystal)

Other smectic liquid crystals shown in TABLE 1 were prepared accordingto known methods.

TABLE 1 (Evaluation of Properties) Smectic Liquid Crystal TransitionTemperature Δn 2 Cr 102 SmA 215 Iso 0.233 3 Cr 117 SmA 178 Iso — 4 Cr119 SmA 175 Iso — 5 Cr 85 (SmC 105) SmA 208 Iso — 7 Cr 85 SmC 86.9 SmA160 N 174 Iso — 8 Cr 123 SmA 200 N 209 Iso — 9 Cr 101 SmA 194 N 198 Iso0.232 13  Cr 75 SmA 101.6 N 113 Iso — Cr: crystal, SmA: smectic A phase,N: nematic phase, and Iso: isotropic phase.(Synthesis of Dichroic Dye)

Dichroic Dye (1-8) was prepared according to the method described inJapanese Laid-Open Patent Publication “Tokkai” No. 2003-192664.

Dichroic Dye (1-14) was prepared according to the method described inJapanese Laid-Open Patent Publication “Tokkai” No. 2005-120334.

Example 2

(Preparation of Liquid Crystal Composition No. 1)

A mixture of 5 mg of Dichroic Liquid Crystal (1-8), 14.8 mg of SmecticLiquid Crystal (1), 75.8 mg of Dual-frequency Switchable Nematic LiquidCrystal (H-1), which is described in Applied Physics Letters, Vol. 25,186-188(1974), and 9.4 mg of Liquid Crystal (H-2),having a negative Δε,was heated on a hot plate of 180° C. for one hour, cooled down to a roomtemperature, and left overnight. Thus, Liquid Crystal Composition No. 1was obtained.

(Preparation of Liquid Crystal Composition No. 2)

Liquid Crystal Composition No. 2 was prepared in the same manner asLiquid Crystal Composition No. 1, except that 1 mg of Dichroic Dye(1-14) was used in the place of 5 mg of Dichroic Dye (1-8).

(Preparation of Liquid Crystal Composition No. 3)

Liquid Crystal Composition No. 3 was prepared in the same manner asLiquid Crystal Composition No. 1, except that Smectic Liquid Crystal (5)was used in the place of Smectic Liquid Crystal (1).

(Preparation of Liquid Crystal Composition No. 4)

Liquid Crystal Composition No. 4 was prepared in the same manner asLiquid Crystal Composition No. 3, except that 1 mg of Dichroic Dye(1-14) was used in the place of 5 mg of Dichroic Dye (1-8).

(Preparation of Liquid Crystal Composition No. 5)

A mixture of 5 mg of Dichroic Liquid Crystal (1-8), 9.7 mg of SmecticLiquid Crystal (3), 9.9 mg of Smectic Liquid Crystal (4), 80.4 mg ofDual-frequency Switchable Nematic Liquid Crystal (H-1) was heated on ahot plate of 180° C. for one hour, cooled down to a room temperature,and left overnight. Thus, Liquid Crystal Composition No. 5 was obtained.

(Preparation of Liquid Crystal Composition No. 6)

Liquid Crystal Composition No. 6 was prepared in the same manner asLiquid Crystal Composition No. 5, except that 1 mg of Dichroic Dye(1-14) was used in the place of 5 mg of Dichroic Dye (1-8).

(Preparation of Liquid Crystal Composition Nos. 7 and 8 for Comparison)

Liquid Crystal Composition No. 7 was prepared in the same manner asLiquid Crystal Composition No. 1, except that only 100 mg ofdual-frequency switchable Nematic Liquid Crystal (H-1) was used as hostliquid crystal. This composition was prepared for comparison.

Liquid Crystal Composition No. 8 was prepared in the same manner asLiquid Crystal Composition No. 7, except that 1 mg of Dichroic Dye(1-14) was used in the place of 5 mg of Dichroic Dye (1-8). Thiscomposition was prepared for comparison.

Example 3

(Production of Liquid Crystal Device)

Each of Liquid crystal device Nos. A to H was produced by pouring eachof Liquid Crystal Composition Nos. 1 to 8 in a commercially availableliquid crystal cell at 180° C. The liquid crystal cell employed was aglass substrate (thickness of 0.7 mm) manufactured by E.H.C. and havingan ITO transparent electrode layer, and had a cell gap of 8 μm and anepoxy resin seal. It is to be noted that any alignment layer was notformed on the ITO transparent electrode layer.

<Evaluation of Dual-Frequency Switching Ability and Memory Ability(Bistability)>

Applying a square wave AC voltage with low frequency (100V, 100 Hz) toeach of Liquid crystal device Nos. A to H, the optical transmittance wasmeasured using a spectrometer, “UV-2400PC” manufacture by ShimazuCorporation. Next, applying a square wave AC voltage with high frequency(100V, 100 kHz) to each of Liquid crystal device Nos. A to H, theoptical transmittance was measured in the same manner. Each of liquidcrystal devices was allowed to stand for a week after turning off thesquare wave AC voltage, and the variation of the optical transmittancewas measured to evaluate its memory ability (bistability). Theevaluation “O” means that no variation in optical transmittance wasfound, and the evaluation “x” means that variation in opticaltransmittance was found.

The obtained results are shown in TABLE 2.

TABLE 2 Liquid Liquid Crystal Crystal Abs Abs Memory Device Composition(100 Hz) (100 kHz) Ability Note A 1 0.10 0.94 ◯ Invention B 2 0.11 1.07◯ Invention C 3 0.11 0.98 ◯ Invention D 4 0.12 1.02 ◯ Invention E 5 0.120.93 ◯ Invention F 6 0.12 0.98 ◯ Invention G 7 0.14 0.73 X Forcomparison H 8 0.14 0.76 X For comparison

From the results shown in TABLE 2, it is understandable that LiquidCrystal Device Nos. A to F gave a higher contrast ratio compared withcomparative examples, Liquid Crystal Device Nos. G and H; and LiquidCrystal Device Nos. A to F could store image information.

INDUSTRIAL APPLICABILITY

The smectic liquid crystal composition of the invention can be employedwidely in producing liquid crystal devices, is especially suitable forbeing employed in producing GH-mode liquid crystal devices. The GH-modeliquid crystal device employing the liquid crystal composition of theinvention can have a high displaying contrast and capable of storingimage information.

1. A smectic liquid crystal composition comprising, at least, a dichroicdye, a dual-frequency switchable nematic liquid crystal and a smecticliquid crystal, wherein a dielectric anisotropy of the compositionchanges from a positive value to a negative value with increasing afrequency of an electric field applied to the composition.
 2. Thesmectic liquid crystal composition of claim 1, wherein the smecticliquid crystal is dual-frequency switchable.
 3. The smectic liquidcrystal composition of claim 1, wherein, being applied a field, adielectric anisotropy of the smectic liquid crystal changes from apositive value to a negative value with increasing a frequency of anapplied electric field.
 4. The smectic liquid crystal composition ofclaim 1, wherein the smectic liquid crystal is a compound presented by afollowing formula (1):T¹-{(D¹)_(e)-L¹}_(m)-(D²)_(k)-T²  Formula (1) where D¹ and D²respectively represent a substituted or non-substituted, arylene group,a heteroarylene group or a divalent cycloaliphatic hydrocarbon group; L¹represents a divalent linking group, T¹ and T² respectively represent asubstituted or non-substituted, alkyl group, alkoxy group,alkoxycarbonyl group, acyl group or acyloxy group, or a halogen atom ora cyano; “e” is an integer from 1 to 3, “m” is an integer from 1 to 3,and “k” is 1 or 2, provided that a total number of D¹ and D² is from 3to 5; when “e” or “k” is more than 2, a plural D¹ or D² may be same ordifferent to each other; and when “m” is more than 2, a plural{(D¹)_(e)-L¹} may be same or different to each other.
 5. The smecticliquid crystal composition of claim 1, capable of transforming to asmectic A phase.
 6. The smectic liquid crystal composition of claim 1,wherein the dichroic dye is a compound having at least one grouprepresented by a following formula (2):-(Het)_(j)-{(B¹)_(p)-(Q¹)_(q)-(B²)_(r)}_(n)-C¹  Formula (2) where “Het”represents an oxygen atom or a sulfur atom; B¹ and B² respectivelyrepresent a substituted or non-substituted arylene group, heteroarylenegroup or divalent cycloaliphatic hydrocarbon group; Q¹ represents adivalent linking group; C¹ represents a substituted or non-substituted,alkyl group, cycloalkyl group, alkoxy group, alkoxycarbonyl group, acylgroup or acyloxy group; j is 0 or 1, p, q and r respectively representan integer from 0 to 5 and n represents an integer from 1 to 3, providedthat a total number of groups represented by B¹ and B² in the formula(2) is from 3 to 10; in case any of p, q and r is equal to or largerthan 2, B¹, Q¹ or B² present in two or more units may be same ordifferent to each other; and, in case n is equal to or larger than 2,{(B¹)_(p)-(Q¹)_(q)-(B²)_(r)} present in two or more units may be same ordifferent to each other.
 7. The smectic liquid crystal composition ofclaim 6, wherein, in the formula (2), “Het” is s sulfur atom.
 8. Thesmectic liquid crystal composition of claim 6, wherein, in the formula(2), “Het” is a sulfur atom, B¹ is a substituted or non-substitutedarylene or heteroarylene group, B² is a cyclohexane-1,4-diyl group, C¹is a substituted or non-substituted alkyl group, j=1, p=2, q=0, r=1 andn=1.
 9. The smectic liquid crystal composition of claim 6, wherein, inthe formula (2), “Het” is a sulfur atom, B¹ is a substituted ornon-substituted arylene or heteroarylene group, B² is acyclohexane-1,4-diyl group, C¹ is a substituted or non-substituted alkylgroup, j=1, p=1, q=0, r=2 and n=1.
 10. The liquid crystal composition ofclaim 1, wherein the dichroic dye is a compound having at least onegroup represented by a following formula (a-1) or a formula (a-2);

wherein S is a sulfur atom, R^(a1), R^(a2), R^(a3), R^(a4), R^(a5),R^(a6), R^(a7), R^(a8), R^(a9), R^(a10), R^(a11) and R^(a12)respectively represent a hydrogen atom or a substituent group; andC^(a1) and C^(a2) respectively represent a substituted ornon-substituted alkyl group.
 11. The smectic liquid crystal compositionof claim 1, wherein the dichroic dye is selected from the groupconsisting of azo dyes, anthraquinone dyes and phenoxazine dyes.
 12. Thesmectic liquid crystal composition of claim 1, wherein the dichroic dyeis a compound represented by a formula (3):

where R¹, R², R³, R⁴, R⁵, R⁶, R⁷ and R⁸ respectively represent ahydrogen atom or a substituent group, provide that at least one is agroup represented by -(Het)_(j)-{(B¹)_(p)-(Q¹)_(q)-(B²)_(r)}_(n)-C¹, inwhich “Het” represents an oxygen atom or a sulfur atom, B¹ and B²respectively represent a substituted or non-substituted arylene group,heteroarylene group or divalent cycloaliphatic hydrocarbon group; Q¹represents a divalent linking group; C¹ represents a substituted ornon-substituted, alkyl group, cycloalkyl group, alkoxy group,alkoxycarbonyl group, acyl group or acyloxy group; j is 0 or 1, p, q andr respectively represent an integer from 0 to 5 and n represents aninteger from 1 to 3, provided that a total number of groups representedby B¹ and B² is from 3 to 10; in case any of p, q and r is equal to orlarger than 2, B¹, Q¹ or B² present in two or more units may be same ordifferent to each other; and, in case n is equal to or larger than 2,{(B¹)_(p)-(Q¹)_(q)-(B²)_(r)} present in two or more units may be same ordifferent to each other.
 13. The smectic liquid crystal composition ofclaim 1, wherein the dichroic dye is a compound represented by a formula(4):

where R¹¹, R¹², R¹³, R¹⁴, R¹⁵, R¹⁶, and R¹⁷ respectively represent ahydrogen atom or a substituent group, provided that at least one is agroup represented by -(Het)_(j)-{(B¹)_(p)-(Q¹)_(q)-(B²)_(r)}_(n)-C¹, inwhich “Het” represents an oxygen atom or a sulfur atom, B¹ and B²respectively represent a substituted or non-substituted arylene group,heteroarylene group or divalent cycloaliphatic hydrocarbon group; Q¹represents a divalent linking group; C¹ represents a substituted ornon-substituted alkyl group, cycloalkyl group, alkoxy group,alkoxycarbonyl group, acyl group or acyloxy group; j is 0 or 1, p, q andr respectively represent an integer from 0 to 5, and n represents aninteger from 1 to 3, provided that a total number of groups representedby B¹ and B² is from 3 to 10; in case any of p, q and r is equal to orlarger than 2, B¹, Q¹ or B² present in two or more units may be same ordifferent to each other; and, in case n is equal to or larger than 2,{(B¹)_(p)-(Q¹)_(q)-(B²)_(r)} present in two or more units may be same ordifferent to each other.
 14. A liquid crystal device comprising: a pairof electrodes of which at least one is a transparent electrode, and alayer between the pair of electrodes comprising a smectic liquid crystalcomposition as set forth in claim
 1. 15. The liquid crystal device ofclaim 14, wherein the layer comprises a polymer and the smectic liquidcrystal composition dispersed in the polymer.
 16. The liquid crystaldevice of claim 14, wherein the layer comprises microcapsulesrespectively comprising the smectic liquid crystal composition.